/Engine/Source/Runtime/Experimental/Chaos/Public/PhysicsProxy/GeometryCollectionPhysicsProxy.h
Build a physics thread cluster parent particle.CollectionClusterIndex_ - the source geometry collection transform index.ChildHandles_ - physics particle handles of the cluster children. `ChildTransformGroupIndices_ - geometry collection indices of the children.  Parameters - uh, yeah... Other parameters.
[Chaos::FPBDRigidClusteredParticleHandle](API\Runtime\Chaos\Chaos\FPBDRigidClusteredParticleHandle) * BuildClusters_Internal ( const uint32 CollectionClusterIndex, [TArray](API\Runtime\Core\Containers\TArray)< [Chaos::FPBDRigidParticleHandle](API\Runtime\Chaos\Chaos\FPBDRigidParticleHandle) * > & ChildHandles, const [TArray](API\Runtime\Core\Containers\TArray)< int32 > & ChildTransformGroupIndices, const [Chaos::FClusterCreationParameters](API\Runtime\Chaos\Chaos\FClusterCreationParameters) & Parameters, const [Chaos::FUniqueIdx](API\Runtime\Chaos\Chaos\FUniqueIdx) * ExistingIndex )